(Justin Jouvenal/The Washington Post)

Dozens of teachers clad in red chanted “Down with The Post lies” during the mid-day protest. Union activists parked a giant, inflatable rat near the entrance to The Post’s headquarters at 15th and L streets in Northwest D.C.

“Absent Kaplan, The Post would be out of business,”said Washington Teachers’ Union president Nathan Saunders.

Saunders said The Post’s editorial board stakes out positions that are in keeping with the general business aims of Kaplan, which offers a range of services including degree programs and standardized test preparation.

Saunders pointed to a Post editorial supporting IMPACT, the D.C. teacher evaluation system, which is partly based on students’ performance on standardized tests.

Kris Coratti, The Post’s communications director, said Kaplan is not involved in The Post’s editorial decision-making.

“The Washington Post is entirely separate and independent from Kaplan and the positions taken in our editorials represent the judgment of the individuals responsible for the page,” Coratti wrote in a statement. “The opinions expressed stand on their own merits and readers, of course, can choose to agree or disagree.”

Kaplan accounted for 62 percent of the Post Co.’s revenue in 2010, according to an annual report. Kaplan has 70 campuses and 100,000 students around the world.

Kaplan has come under scrutiny in recent years. A government probe recently found employees pushed students to take on loans, regardless of whether they could afford them. Four have filed whistleblower lawsuits, accusing the company of breaking the law to recruit more students. Kaplan says the charges are baseless.

“I don’t believe we’re running an unethical company,” Jeff Conlon, chief executive of Kaplan’s higher-education unit, said in a Washington Post article earlier this month. “I’ve been with Kaplan 18 years, and in that time I’ve been surrounded by co-workers, peers, staff and executives who firmly believe that doing things right for the students is the best way to long-term success.”

Reporter Bill Turque contributed to this report.